Nitronickelate
The nitronickelates are a class of chemical compounds containing a nickel atom complexed by nitro groups, –NO2.
Nickel can be in a +2 or +3 oxidation state. There can be five, or six, nitro groups per nickel atom. They can be considered the double nitrites of nickel nitrite.
| formula | name | structure | Remarks | references |
| Rb3 | trirubidium pentanitronickelate | |||
| Cs3 | tricaesium pentanitronickelate | dark red, formed from caesium nitrite and nickel nitrite in water | ||
| K3·KNO2 | potassium pentanitronickelate potassium nitrite | monoclinic, a = 7.240 Å, b = 10.946 Å, c = 7.120 Å, β = 98.086°; Z = 2; 4 nitro groups bonded to Ni by N, 1 by O | formed by heating monohydrate at 100 °C dark purple; hygroscopic | |
| K4·H2O | potassium hexanitronickelate monohydrate | hexagonal, a = 7.634 Å, c = 22.45 Å, Z = 3; nitro groups bonded to Ni via N; water not coordinated | formed from KNO2 and NiCl2 mix in water; orange brown; stable in vacuum | |
| K2Ca | potassium calcium hexanitronickelate | cubic, a = 10.31 Å, Z = 4 | buff | |
| K2Sr | potassium strontium hexanitronickelate | cubic, a = 10.5063 Å, Z = 4, density = 2.867 g/cm3 | brown yellow | |
| K2Ba | potassium barium hexanitronickelate | cubic Fm3, a = 10.7800 Å, Z = 4, density = 2.918 g/cm3 | brown yellow | |
| K2Pb | potassium lead hexanitronickelate | cubic Fm3, a = 10.577 Å, Z = 4, density = 3.480 g/cm3: No NO2 group disorder | buff colour | |
| N4 | tetramethylammonium nickel nitrite TMNIN | hexagonal perovskite P''m''1, a = 9.103 Å, c = 7.082 Å, V = 508.2 Å3, Z = 2, density = 1.770 g/cm3; all nitros are bidentate, nickel either links to N or O of the NO2, forming a chain of nickel alternating with ONO | yellow brown; one-dimensional Heisenberg antiferromagnet; Haldane material; phase transitions at 409.1 and 428.4 K due to rotation of N4 |